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I have a DC-DC converter that I want to repair. Unfortunately I cannot identify 2 SMD components from the drive circuitry. I am hoping some of you can help me identify what they are so I can have the complete schematic and find replacements.

I attached a hand-made schematic of the drive section as well as a photo of the PCB.

enter image description here enter image description here

Thank you.

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  • \$\begingroup\$ Some NPN transistor that is a complement to the 2SA1020. \$\endgroup\$
    – τεκ
    Commented Jan 24, 2018 at 18:25
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    \$\begingroup\$ That’s poor soldering - just waiting to cause shorts... \$\endgroup\$
    – Solar Mike
    Commented Jan 24, 2018 at 18:36
  • \$\begingroup\$ The 2SA1020 is obsolete anyway, so get something that exceeds its specs, and its complement. \$\endgroup\$
    – τεκ
    Commented Jan 24, 2018 at 18:38
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    \$\begingroup\$ 2SA1020G is a recognised part number, searching for data and suppliers should be easy. The other is not ... TEK's suggestion might be the way forward, start from 2SA1020 and find its recommended complement. \$\endgroup\$
    – user16324
    Commented Jan 24, 2018 at 18:40
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    \$\begingroup\$ The real 2SA1020 is not made in SOT-89 anyway, that's a Chinese hybrid using something like the 2SA1020 die in a non standard SOT-89 package. It does not conform to EIAJ JIS-C-7102. 2SC2655 is the complement to the 2SA1020. \$\endgroup\$ Commented Jan 24, 2018 at 18:40

2 Answers 2

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  • verify transistors OK with DMM diode test BC & BE

    enter image description here

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Now is all clear. I checked the transistors: both are OK. Lucky me !

2SA1020G comes in SOT-89 package also (is written in the datasheet). They might be obsolete but are more than enough for the application (driving the MOSFETs with under 20V when they have a Vds=50V). No point to replace them if they work.

I replaced all power MOSFETs (16) and some Zenner surge suppressors with higher voltage rating versions and some burned resistors and the DC converter works again. I thank everyone for helping me identify those transistors.

BTW: To who is curious, this is the DC-DC converter from HI Voltage to Battery Voltage from the MPI 5,5K Hybrid Inverter made by MPP Solar. Was partially my fault that it failed. I set a 61V battery charging voltage, not knowing the Zenner surge suppressors across the MOSFETs were rated to 60V max. A bug in the software and Blam ! :) Now I know.

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